1. Field of the Invention
The present invention relates to a mounting structure of a semiconductor device which can be easily detached from a wiring substrate after being mounted on the wiring substrate and a mounting method thereof.
2. Description of the Related Art
Conventionally, a method is known where a semiconductor chip is mounted on a wiring substrate through solder balls densely provided on one surface of the semiconductor chip. In such a conventional mounting structure of a semiconductor device, resin referred to as underfill is filled into the gap between the semiconductor chip and the wiring substrate. For example, Japanese Patent Application Laid-open No. Hei 10-284635 discloses a semiconductor device in which filling resin is embedded in a gap between a semiconductor chip and a substrate so as to cover solder balls.
With reference to FIG. 7, in such a conventional semiconductor device, a semiconductor chip 21 and a wiring substrate 25 are connected to each other by welded solder balls 26 of the semiconductor chip 21. Further, resin 29 is injected into the gap between the semiconductor chip 21 and the wiring substrate 25 so as to cover the solder balls 26. The resin 29 is injected for the purpose of alleviating the thermal stress caused by the difference in the coefficient of thermal expansion between the semiconductor chip 21 and the wiring substrate 25. The semiconductor chip 21 and the wiring substrate 25 repeat expansion and contraction by heat generated by operations (on/off operation) of the device. However, the coefficient of thermal expansion of the semiconductor chip 21 is about 3.5 ppm whereas the coefficient of thermal expansion of the wiring substrate 25 is about 16 ppm in case of a printed board and about 8 ppm in case of an alumina substrate. Due to this difference in the coefficient of thermal expansion between the semiconductor chip 21 and the wiring substrate 25, the solder balls 26 are alternately subject to compressive stress and tensile stress. As a result, the solder balls 26 are broken at an early stage due to thermal fatigue, which causes electric disconnection, resulting in a signal transmission stop or a power supply stop.
Therefore, by filling the resin 29 into the gap between the semiconductor chip 21 and the wiring substrate 25 so as to cover the solder balls 26. The resin 29 alleviates stress on the solder balls 26. This suppresses the deterioration of the solder balls 26, and the reliability of the connection between the semiconductor chip 21 and the wiring substrate 25 is improved. It is to be noted that epoxy-based resin is mainly used as the resin 29.
However, in the conventional semiconductor device described above, since the semiconductor chip 21 and the wiring substrate 25 are mechanically firmly bonded to each other with the resin 29, once the semiconductor chip 21 is attached to the wiring substrate 25, the semiconductor chip 21 can not be easily detached from the wiring substrate 25. Therefore, there has been a problem in that the semiconductor chip 21 can not be easily replaced and the maintainability is lowered.
An object of the present invention is to provide a mounting structure of a semiconductor device in which a semiconductor chip can be detached from a wiring substrate and high reliability is realized.
According to the present invention, a mounting structure of a semiconductor device with excellent connection reliability can alleviate the stress on solder balls caused by the difference in the coefficient of thermal expansion between a semiconductor chip and a wiring substrate when the semiconductor chip is mounted on the wiring substrate.
Further, according to the present invention, amounting structure of a semiconductor device with excellent maintainability can be provided in which a semiconductor chip can be easily detached from a wiring substrate after the semiconductor chip has been mounted on the wiring substrate.